1. Field of the Invention
The present invention relates to a nacelle roof structure of a wind turbine generator.
2. Description of Related Art
A wind turbine generator is designed to generate electric power using a generator which is driven as a rotor head equipped with wind turbine blades is rotated by wind power and the rotation is speeded up by a gear box. The rotor head is installed on an end portion of a nacelle which, being mounted on a wind turbine tower, is capable of yawing, and is supported in such a way as to be able to rotate around a substantially horizontal transverse rotation axis.
A nacelle cover adapted to cover the nacelle of the wind turbine generator is generally constructed by connecting plural fiber reinforced plastic (FRP) panels and a connection structure for the panels needs to be designed to be able to prevent infiltration of rainwater from outside the nacelle cover.
Also, panel connections are generally joined by bolts, but when the nacelle cover is subjected to external forces caused by wind pressure, snow cover, or the like, the panel connections joined by bolts become the weakest part in terms of strength. Therefore, the panel connections need to have a structure free from high material strain.
In a conventional nacelle roof structure shown in FIG. 6, a roofing member 3 adapted to cover a top face of a nacelle 2 is configured by integrating roof shingles 3L and 3R which divide the nacelle into two parts—right and left parts—in a width direction and is mounted by being connected with upper end portions of nacelle side-walls 4. Generally, the nacelle 2 is shaped substantially as a rectangular parallelepiped. When viewed from above, the nacelle 2 is rectangular in planar view and the long edge corresponds to a front-rear direction which coincides with a main-shaft direction while the short edge corresponds to a width direction.
The roof shingles 3L and 3R are joined by fastening respective flanges 3a by bolt connection as shown in FIG. 6, (b) and a joining line L between the roof shingles 3L and 3R extends to a length substantially equal to that of the long edge (main-shaft direction) of the nacelle 2.
In this case, the flanges 3a joining together the roof shingles 3L and 3R are set at such an angle that a joined portion of the roofing member 3 will be slightly higher when fastening is complete. That is, the flanges 3a at the joint are not set at right angles to the roof shingles 3L and 3R, but have an angle α smaller than 90 degrees (α<90 degrees) by deviating slightly from a right angle such that the joint bent by fastening will be convex upward with respect to an outer periphery of the nacelle 2.
Also, regarding typical structures for wall panel connections, for example, a technique disclosed in Japanese Unexamined Patent Application, Publication No. Hei 7-62758 is known.
Recently, wind turbine generators have been growing in size along with increases in output power, and naturally the shape of the nacelle 2 has been becoming larger. Consequently, the length of the joining line L of the roof shingles 3L and 3R which make up the roofing member 3 is increased in the main-shaft direction (front-rear direction of the nacelle), and furthermore the length from the joining line L to the nacelle side-walls 4 is increased as well.
On the other hand, since no support member is connected to the roofing member 3 except the nacelle side-walls 4, stresses will concentrate on a bolt-connected flange coupling under the load of snow cover or the like.
When the roofing member 3 becomes larger along with the nacelle shape, the dimension from the joining line L to the nacelle side-walls 4 increases and becomes longer, making it necessary to deal with stress concentration more strictly, and it is feared that the flange coupling described above could be broken in the worst case.
Furthermore, when the roofing member 3 increases in size, the shape of the roof shingles 3L and 3R equipped with the flanges 3a become larger as well due to the right/left two-block structure. Moreover, since the flanges 3a which protrude also grow in size, it becomes difficult to efficiently perform loading and subsequent transport from a manufacturing plant to an installation site.
Also, for example, during maintenance after installation of the wind turbine generator, it becomes necessary to perform the operation of carrying large equipment (including a gear box and generator) installed inside the nacelle cover out of the nacelle cover in a high-elevation, high-wind environment. For that, it is necessary that the roofing member 3 which is part of the nacelle cover of the wind turbine generator is structured to be able to be removed and reinstalled easily. In particular, the roofing member 3 which makes up roof part of the nacelle cover needs to be made removable to take sufficient measures against intrusion of rain water.
On the other hand, the wall panel connection structure disclosed in Japanese Unexamined Patent Application, Publication No. Hei 7-62758 is a connection structure for wall panels used in housing and is different from a nacelle roof structure of a wind turbine generator, which uses fiber reinforced plastic panels.